1. Technical Field
The present invention relates to a droplet ejecting apparatus and ejection abnormality detecting/determining method for a droplet ejecting head.
2. Related Art
The ink jet printer, as a droplet ejecting apparatus, forms an image on a predetermined paper by ejecting ink droplets from a plurality of nozzles. The ink jet printer has a print head (ink jet head) provided with a plurality of nozzles. However, clogging possibly takes place at certain nozzles due to ink viscosity increase, air bubble mixing, dust or paper powder adhesion or the like, resulting in impossible ink ejection. Nozzle clogging causes dot missing in the printed image, raising a cause of image deterioration.
Conventionally, there has been devised, as a method of detecting such an ejection abnormality of ink droplets (hereinafter referred also to as “dot missing”), a method of optically detecting a state that an ink droplet is not to be ejected at the ink jet head nozzles (ink droplet ejection abnormality) (e.g. JP-A-8-309963, etc.). This method makes it possible to specify a nozzle causing dot missing (ejection abnormality).
However, in the above optical dot-missing (droplet ejection abnormality) detecting method, a detector including a light source and optical sensor is attached on the droplet ejecting apparatus (e.g. ink jet printer). In this detection method, there is generally a problem that the light source and the optical sensor must be set up with accuracy so that the droplet ejected at the droplet ejection head (ink jet head) nozzle can pass through between the light source and the optical sensor, to thereby block the light between the light source and the optical sensor. In addition, such a detector is usually expensive, which problematically raises the manufacturing cost of ink jet printers. Furthermore, there is a possibility that the ink mist from the nozzles and paper powder of printing papers, etc. cause contamination in the light-source output part and optical-sensor detector part, resulting in a problematic reliability in the detector.
Meanwhile, in the above optical type dot-missing detecting method, although detection is possible for dot missing at the nozzles, i.e., ink-droplet ejection abnormality (non-ejection), the cause of dot missing (ejection abnormality) cannot be specified (determined) depending upon the detection result. Thus, there is a problem of impossibility to select and carry out a suitable recovery process corresponding to the cause of dot missing. Consequently, despite the state being recoverable by a wiping process for example, ink is pump-out from the ink jet head, thus increasing waste ink (useless ink). Otherwise, instead of doing the proper recovery process, a plurality of recovery steps is carried out to thereby lower or degrade the throughput over the ink jet printer (droplet ejecting apparatus).
It is an object of the present invention to provide a droplet ejecting apparatus and ejection abnormality detecting/determining method for a droplet ejecting head that, depending upon a capacitance change on a vibration plate of an actuator after droplet ejecting operation, the period of residual vibration on the vibration plate is measured to thereby detect an ejection abnormality on the droplet ejection head and determine a cause of the ejection abnormality.